Articular cartilage - Hyaline cartilage

Cartilage is characterized by chondrocytes (cartilage cells) which lie within and produce the cartilage ground substance (extracellular matrix ECM), as seen in all types of connective tissue. Depending on the type and amount of fibers in the ECM, three types of cartilage are distinguished: hyaline, elastic, and fibrocartilage.

In adults, all types of cartilage are largely devoid of blood vessels; their supply occurs through diffusion processes from the vascular perichondrium or, in the case of hyaline articular cartilage, directly from the joint fluid (synovia) produced by the joint capsule.

Specific to all three types of cartilage is its high compressive elasticity, viscoelastic deformability (bend-resistant), and resistance to shear forces.

Hyaline Articular Cartilage

Function

Hyaline cartilage forms the protective layer of the highly sensitive and well-innervated bones in all synovial joints. It absorbs and cushions impact and compression forces. By minimizing friction forces, it ensures smooth joint movement, which is heavily supported by the synovial fluid.

Structure and Components

The morphological structure is organized within 4 distinct zones:

• Zone I: Superficial cartilage zone (approx. 5%), main task: absorb shear forces and reduce friction

  This is the thinnest of the 4 zones; water binding is at its highest; coated with synovial fluid; collagen fibrils are thinnest and run parallel to the joint surface

• Zone II: Middle cartilage zone or transitional zone (approx. 15%), main task: not specifically known

  Collagen fibrils run obliquely to the surface, forming arches (arcades)

• Zone III: Deep or radial cartilage zone (approx. 40 – 60%), main task: absorption of compression forces

  Thickest layer; collagen fibrils run perpendicular to the joint surface; contains the most active cartilage cells

• Zone IV: Calcified cartilage zone (approx. 30%), main task: anchoring the articular cartilage to the bone

  Relatively thin layer; the boundary between the deep and calcified cartilage zones is formed by the tidemark; collagen fibrils pass through the tidemark into the calcified zone, connecting the softer, deformable cartilage with the hard, non-deformable bone; anchoring and stabilizing the articular cartilage to the bone

Due to its negative charge, the ground substance of hyaline cartilage can store a vast amount of water (60 – 80%). The strong bond between water and collagen fibers creates a homogeneous network that exceptionally resists compression loads—the primary task of hyaline articular cartilage.

The cartilage cells (chondrocytes) synthesize the necessary components of the ECM. However, synthesis activities decrease significantly after the growth phase. They also depend on the quality and nutrient supply of the synovial fluid, the matrix composition, and the subchondral, well-perfused bone. This poses a challenge, as cartilage has virtually no blood vessels for nutrient supply. Nutrients reach the cells primarily through diffusion and osmosis. During compression, water not only moves within the cartilage but also enters the synovial fluid and the subchondral bone. When the pressure is released, the fluid flows back from the underlying bone into the cartilage, carrying the essential nutrients required to maintain healthy articular cartilage.

Alternating cycles of pressure and release actively promote the transport and exchange of these vital substances.

What Does Our Articular Cartilage Need?

To maintain itself, healthy articular cartilage requires constant synthesis and regeneration of its fibrils and ground substance. The turnover time of hyaluronic acid is just 2 – 4 days, whereas for fibrils, it is significantly longer. Keep in mind, the turnover time for collagen fibers is 300 to 500 days—a very long time. Chronic underuse is therefore the most detrimental factor for the function and stability of our articular cartilage. And this is exactly what our modern, sedentary lifestyle often brings with it.

What Effect Does Training Have on Cartilage Tissue?

Training has a massive impact on the structure of the cartilage: the micellar arrangement (micelles: aggregated molecular complexes) is improved after training, leading to an increase in tensile strength. Cartilage tissue responds to training stimuli with a reversible hypertrophy (an increase in chondrocytes). Among other benefits, this reduces joint incongruence by expanding the contact surfaces, thereby improving compressive elasticity and shock absorption.

However, training and exercise do not just improve the adaptability of the cartilage tissue: stronger skeletal muscles and better technique/coordination also ease the movement patterns under higher loads, protecting both your tissue and your body!

Osteoarthritis & Co.

Degenerative changes (wear and tear) are referred to as osteoarthritis. Causes are believed to include decreased alternating cycles of loading and unloading, increasing calcification of the cartilage tissue, and physical trauma.

Immobilization—due to various causes—leads to rapid and severe demineralization, causing pathophysiological changes in our cartilage and bone tissue.

Therapy

The physiotherapists and osteopaths at BodyLab are experts in anatomical and physiological conditions. In the event of injury or discomfort, they know exactly which therapeutic options will deliver results. We are happy to advise and guide you on training possibilities. If active training is not yet possible (after surgery or injury) or no longer possible, passive joint techniques—sometimes utilizing compression or traction—can improve the quality and function of the articular cartilage as well as the entire joint as a functional unit, thereby reducing pain and discomfort.

Once again, the golden rule applies: Life is movement!

Whenever you need us, we are here to support you!

Your BodyLab Team, your go-to partner for movement and pain relief

Osteopathy and Physiotherapy | Rehabilitation and Training

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Learn more about our menisci in another blog post.